title: Protein-protein interaction regulates the direction of catalysis and electron transfer in a redox enzyme complex.
abstract: Protein-protein interactions are well-known to regulate enzyme activity in cell signaling and metabolism. Here, we show that protein-protein interactions regulate the activity of a respiratory-chain enzyme, CymA, by changing the direction or bias of catalysis. CymA, a member of the widespread NapC/NirT superfamily, is a menaquinol-7 (MQ-7) dehydrogenase that donates electrons to several distinct terminal reductases in the versatile respiratory network of Shewanella oneidensis . We report the incorporation of CymA within solid-supported membranes that mimic the inner membrane architecture of S. oneidensis . Quartz-crystal microbalance with dissipation (QCM-D) resolved the formation of a stable complex between CymA and one of its native redox partners, flavocytochrome c3 (Fcc3) fumarate reductase. Cyclic voltammetry revealed that CymA alone could only reduce MQ-7, while the CymA-Fcc3 complex catalyzed the reaction required to support anaerobic respiration, the oxidation of MQ-7. We propose that MQ-7 oxidation in CymA is limited by electron transfer to the hemes and that complex formation with Fcc3 facilitates the electron-transfer rate along the heme redox chain. These results reveal a yet unexplored mechanism by which bacteria can regulate multibranched respiratory networks through protein-protein interactions.
authors.affiliation: School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Duncan G G
authors.initials: DG
authors.lastname: McMillan
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: Marritt
authors.forename: Mackenzie A
authors.initials: MA
authors.lastname: Firer-Sherwood
authors.forename: Liang
authors.initials: L
authors.lastname: Shi
authors.forename: David J
authors.initials: DJ
authors.lastname: Richardson
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Evans
authors.forename: Sean J
authors.initials: SJ
authors.lastname: Elliott
authors.forename: Julea N
authors.initials: JN
authors.lastname: Butt
authors.forename: Lars J C
authors.initials: LJ
authors.lastname: Jeuken
mesh_terms: D055162:Biocatalysis; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D004579:Electron Transport; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011485:Protein Binding; D020592:Shewanella / Q000201:enzymology
chemical_list: D003574:Cytochrome c Group; C017165:cytochrome c(3)